The present invention relates to a latex with two distinct particle size ranges and is useful as a binder in coatings formulations.
The ability to prepare polymer dispersions (latexes) having high solids content (>55 weight percent) is desirable because higher relative amounts of water increase costs and storage requirements with no added benefit. Moreover, a high solids latex allows increased flexibility in the paint making process because more water is available to the paint maker at higher pigment volume concentration (PVC). However, as the percent solids of the polymer increases, the viscosity increases and the polymer particles tend to agglomerate. In response to these problems, researchers have prepared dispersions with bimodal particle size, larger particle size, and broad particle size distributions. However, efforts that have achieved success in improving solids content tend to do so at the expense of hiding.
U.S. Pat. No. 6,818,697 describes a bimodal distribution of phosphoethyl methacrylate-containing acrylic polymer particles that allows the formulator to increase the solids content of the latex without sacrificing stain blocking, block resistance or shear stability. Nevertheless, maintaining hiding efficiency continues to be a challenge for high solids latexes. Accordingly, there is a need to make high solids emulsions with an even greater improvement in hiding.